Sex Speeds Up Evolution, Study Finds

Scientifically, it appears to make little sense. It can be time-consuming and exhausting. It's not even essential to reproduction, at least not to lower organisms such as microbes and certain fungi, which can multiply without sex.

To demonstrate this, a team of scientists created a mutant strain of yeast that, unlike normal yeast, was unable to divide into the sexual spores that allow yeast to engage in sexual reproduction. Yeast can reproduce either sexually or asexually.

When testing this mutant strain in stress-free conditions, the scientists found that it performed as well as normal yeast. In more extreme conditions, however, the normal yeast grew faster than the asexual mutants.

This shows "unequivocally that sex allows for more rapid evolution," said Matthew Goddard of the School of Biological Sciences at the University of Auckland in New Zealand.

Goddard led the study, which is reported in this week's issue of the science journal Nature.

An Evolutionary Function

Going back to the 19th century, scientists have proposed that sexual reproduction makes natural selection more effective because it increases genetic variation.

However, since then, evolutionary biologists have struggled to find a simple and general explanation for why sex comes in handy when it comes to the survival of the fittest.

"Experiments with sex have been very hard to conduct," Goddard said. "In an experiment, one needs to hold all else constant, apart from the aspect of interest. This means that no higher organisms can be used, since they have to have sex to reproduce and therefore provide no asexual control."

Goddard and colleagues instead turned to a single-celled organism, yeast, to test the idea that sex allows populations to adapt to new conditions more rapidly than asexual populations.